In computer networking, the term “multicast” refers to the delivery of a message or information to a group of destination computers simultaneously in a single transmission from the source creating copies automatically in other network elements, such as routers, only when the topology of the network requires it. Multicast is most commonly implemented in Internet Protocol (IP) multicast, which is often employed in IP applications of streaming media and Internet television. In IP multicast the implementation of the multicast concept occurs at the IP routing level, where routers create optimal distribution paths for datagrams sent to a multicast destination address. At the Data Link Layer, multicast describes one-to-many distribution such as Ethernet multicast addressing, Asynchronous Transfer Mode (ATM) point-to-multipoint virtual circuits (P2MP) or Infiniband multicast.
Shortest Path Bridging (SPB) is a transport network protocol that provides logical Ethernet networks on native Ethernet infrastructure using a link state protocol to advertise both topology and logical network membership. Packets are encapsulated at the edge of an SPB network either in mac-in-mac 802.1 ah or tagged 802.1 Q/802.1 ad frames and transported only to other members of the logical network. Unicast and multicast are supported and all routing is on symmetric shortest paths. Many equal cost shortest paths are supported.
Wireless LAN (WLAN) is a technology that extends Local Area Network (LAN) to wireless users. The prevailing WLAN technology today is so-called Overlay WLAN model, in which wireless radio signal terminates in Access Points (APs), and then wireless data is passed to Wireless Controllers (WCs) where data packets are brought into LAN. In this model, WCs contain both wireless network control and data forwarding information, and behave as both network controllers and data forwarders.
One embodiment of a Wireless LAN Split Plane technology separates the wireless LAN control and data forwarding functionality. While keeping the control functions in WCs, the forwarding task is offloaded to Wireless Switching Points (WSPs), which normally are integrated into traditional switches and routers. By separating control and switching functionalities, WLAN network switching bottlenecks are removed and performance is greatly improved. Therefore, it is superior solution compared to the traditional Overlay WLAN model.
One of the technical challenge of the WLAN Split Plane solution is to support wireless IP multicast functions. The initial Split Plane IP multicast solution was based on IGMP snooping as part of the Protocol Independent Multicast (PIM) protocol.
PIM is a multicast routing protocol for Internet Protocol (IP) networks that provide one-to-many and many-to-many distribution of data over a LAN, WAN or the Internet. It is termed protocol-independent because PIM does not include its own topology discovery mechanism, but instead uses routing information supplied by other traditional routing protocols such as, Open Shortest Path First (OSPF), Border Gateway Protocol (BGP) and the like. One version of PIM is Protocol Independent Multicast—Sparse Mode (PIM-SM) which can use the underlying unicast routing information base or a separate multicast-capable routing information base. PIM-SM is a protocol for efficiently routing Internet Protocol (IP) packets to multicast groups that may span wide-area and inter-domain Internets. The protocol is named protocol-independent because it is not dependent on any particular unicast routing protocol for topology discovery, and sparse-mode because it is suitable for groups where a very low percentage of the nodes (and their routers) will subscribe to the multicast session. Unlike earlier dense-mode multicast routing protocols such as DVMRP and dense multicast routing which flooded packets across the network and then pruned off branches where there were no receivers, PIM-SM explicitly constructs a tree from each sender to the receivers in the multicast group. PIM-SM builds unidirectional shared tree rooted at a Rendezvous Point (RP) per group and optionally creates shortest-path trees per source. PIM-SM works in traditional IP networks. PIM-SM traditionally is not defined or extended over SPB networks as conventional SPB networks have no knowledge of rendezvous points or rooted multicast if users are running a PIM based IP multicast network, WSPs have to depend on an external device running PIM to integrate the WSP into PIM networks.
Another version of PIM is known as PIM source specific multicast (PIM-SSM). PIM-SSM builds trees that are routed in a single source. In PIM-SS, an IP datagram is transmitted by a source (S) to an SSM destination address (G). Receivers can receive the datagram by subscribing to channel (S,G). The term PIM is used herein to refer to either or both of PIM-SM and PIM-SSM.
Normally the external PIM boxes work as IGMP queriers. To be more specific, if a WSP is a Mobility VLAN server, the VLAN that serves mobility needs to have IGMP snoop turned on. If that is a PIM network, then the WSP needs to connect to other switches/routers, which have PIM enabled, to bring it into PIM networks.
A majority of enterprise customers deploy PIM based IP multicast network. This invention provides a method that integrates WLAN split Plane solution with existing IP Multicast PIM technology on WSPs without the need of deploying extra PIM routers in the network. This helps PIM users to lower their network deployment cost.